The CLR's DEVPATH feature has always been broken and its brokeness varied over the years, but for my purposes it was a very useful feature. However with .NET .4.5 Microsoft decided to up the ante. If you have configured your .NET 4.5 runtime as a "developer installation", ngen will fail to generate native images for framework assemblies. This means that after Windows Update services mscorlib.dll, no native images will be used anymore.

Obviously you can work around this by editing the machine.config and re-running ngen, but that is a bit of a pain so decided to hack together a workaround.

The basic idea is to have a DLL that gets injected into (nearly) every process and patches mscoree.dll to make CreateConfigStream read developer-machine.config instead of machine.config if the DEVPATH environment variable is set.

The source and binaries are available here. Like the Microsoft DEVPATH code, this is untested so there is no warranty and use at your own risk. Bug reports are welcome of course.

There is no installer and there are no installation instructions, because frankly, if you don't know how to install it you probably shouldn't be doing so anyway..

The overhead is fairly low. If you don't have DEVPATH set the DLL will immediately unload again. The file size is only 3KB and in memory it will only use a single 4KB page.

Do the "no serialization" check before calling Serialization.AddAutomagicSerialization() to avoid triggering the class initializer (which will try to load SerializableAttribute, which is not available everywhere).

IKVM.Reflection: Made AssemblyBuilder.__AssemblyFlags a read/write property and marked __SetAssemblyFlags() obsolete.

IKVM.Reflection: Bug fix. Changed AssemblyName.ProcessorArchitecture to match (weird) .NET behavior. When reading the property it returns the architecture of the PE file, not the field from the AssemblyDef record.

IKVM.Reflection: Throw InvalidOperationException when MethodBuilder.DefineGenericParameters() is called a second time.

IKVM.Reflection: Added UniverseOptions.DontProvideAutomaticDefaultConstructor to disable the "helpful" creation of a default constructor.

IKVM.Reflection: Fixed ExportedType resolver to support types defined in another module in this assembly.

IKVM.Reflection: Added the Assembly.ModuleResolve event.

IKVM.Reflection: If missing member resolution is enabled, automatically create missing modules as needed.

IKVM.Reflection: When calling MethodBuilder.DefineParameter() multiple times for the same parameter, we would (sometimes) not store the ParameterBuilder and this would cause the resulting PE file to be corrupt. Now we store the duplicate Param records like SRE does.

IKVM.Reflection: Added UniverseOptions.MetadataOnly.

IKVM.Reflection: Made user string heap loading lazy.

IKVM.Reflection: Bug fix. If SizeOfOptionalHeader is greater than the number of bytes we read from the optional header, we should skip the additional bytes. If it is less, the image is invalid. Thanks to Jb Evain.

Removed org.omg.PortableInterceptor.UNKNOWN class, that is not part of [Open]JDK rt.jar.

Added ZipFile constructor that was added in Java 7.

Add support for running with headless awt toolkit.

Changed ikvmc to apply custom attribute annotations on annotation types to the corresponding custom attribute that is generated (and allow AttributeUsageAttribute to override the default AttributeUsageAttribute generated from the @Target annotation).

Added app.config files for executables to allow them to run on .NET 4.5 on Windows 8 without triggering the .NET 3.5 auto download.

Added (optional) support for building without System.Core.dll dependency.

In Java static initializers can deadlock, on .NET some threads can see uninitialized state in cases where deadlock would occur on the JVM.

JNI

Only supported in the default AppDomain.

Only the JNICALL calling convention is supported! (On Windows, HotSpot appears to also support the cdecl calling convention).

Cannot call string contructors on already existing string instances

A few limitations in Invocation API support

The Invocation API is only supported when running on .NET.

JNI_CreateJavaVM: init options "-verbose[:class|:gc|:jni]", "vfprintf", "exit" and "abort" are not implemented. The JDK 1.1 version of JavaVMInitArgs isn't supported.

JNI_GetDefaultJavaVMInitArgs not implemented

JNI_GetCreatedJavaVMs only returns the JavaVM if the VM was started through JNI or a JNI call that retrieves the JavaVM has already occurred.

DestroyJVM is only partially implemented (it waits until there are no more non-daemon Java threads and then returns JNI_ERR).

DetachCurrentThread doesn't release monitors held by the thread.

Native libraries are never unloaded (because code unloading is not supported).

The JVM allows any reference type to be passed where an interface reference is expected (and to store any reference type in an interface reference type field), on IKVM this results in an IncompatibleClassChangeError.

monitorenter / monitorexit cannot be used on unitialized this reference.

Floating point is not fully spec compliant.

A method returning a boolean that returns an integer other than 0 or 1 behaves differently (this also applies to byte/char/short and for method parameters).

Synchronized blocks are not async exception safe.

Ghost arrays don't throw ArrayStoreException when you store an object that doesn't implement the ghost interface.

Class loading is more eager than on the reference VM.

Interface implementation methods are never really final (interface can be reimplemented by .NET subclasses).

JSR-133 finalization spec change is not fully implemented. The JSR-133 changes dictate that an object should not be finalized unless the Object constructor has run successfully, but this isn't implemented.

If a class with a finalizer and static initializer allocates instances of itself in the static initializer and the static initializer subsequently fails, the .NET runtime may abort the application when trying to finalize the objects.

Static Compiler (ikvmc)

Some subtle differences with ikvmc compiled code for public members inherited from non-public base classes (so called "access stubs"). Because the access stub lives in a derived class, when accessing a member in a base class, the derived cctor will be run whereas java (and ikvm) only runs the base cctor.

Try blocks around base class ctor invocation result in unverifiable code (no known compilers produce this type of code).

Try/catch blocks before base class ctor invocation result in unverifiable code (this actually happens with the Eclipse compiler when you pass a class literal to the base class ctor and compile with -target 1.4).

Only code compiled together during a single compilation fully obeys the JLS binary compatibility rules.

Class Library

Most class library code is based on OpenJDK 7u6 build 24. Below is a list of divergences and IKVM.NET specific implementation notes.

Partial implementation. JPEGs can be read and written and there is limited metadata support.

javax.management

Limited implementation.

javax.print

There is a Win32 specific printing implementation. Not supported.

javax.script

ECMAScript implementation is not included.

javax.smartcardio

Not implemented.

javax.sound

Not implemented.

javax.swing

Not supported.

javax.tools

Not supported.

org.ietfs.jgss

Not implemented.

sun.jdbc.odbc

Implementation based on .NET ODBC managed provider.

sun.net.www.content.audio

Audio content handlers not implemented.

sun.net.www.content.image

Not supported.

The entire public API is available, so "Not implemented." for javax.smartcardio, for example, means that the API is there but there is no back-end to provide the actual smartcard communication support. "Not supported." means that the code is there and probably works at least somewhat, but that I'm less likely to fix bugs reported in these areas, but patches are welcome, of course.

This blog entry was originally posted on June 23, 2011, but was deleted as Oracle asked me to take it down while they investigate. After more than a year, the issue still has not been addressed, so I notified Oracle that I wanted to repost the blog entry and received no response. -- Jeroen

In one of last year's updates of JDK 6 the cloning vulnerability was fixed in a hackish, but clever and safe way. Now in JDK 7 they try to fix it by overriding Object.clone() with a version that simply throws CloneNotSupportedException. The only problem is, in Java (and .NET too) overriding a method is not a safe way to make the base class method unavailable.

The (still) not so well known ACC_SUPER flag allows you (when it isn't set) to call arbitrary (accessible) methods in your super class hierarchy. So Thread.clone() can be skipped and Object.clone() can be called from any Thread subclass that doesn't have the ACC_SUPER flag set.

I forgot to include the fix for transient constant static final fields in the previous release candidate and a new bug was reported in how IKVM.Reflection writes the debug PE header that causes problems with Visual Studio 2012's code coverage tools.